The present invention relates to a glass substrate for a data recording medium of a data recording apparatus such as a hard disk. For example, the present invention relates to a glass substrate used in a magnetic disk, a magneto-optical disk, an optical disk. The present invention also relates to a method for manufacturing such a glass substrate.
Typically, a magnetic disk, which is a type of data recording media, is used, for example, in a hard disk drive. Such a magnetic disk is manufactured by forming magnetic layers and other layers on the surface of a glass substrate for data storing medium. The hard disk drive has a magnetic head (hereinafter referred to as a head) for reading data magnetically recorded on the magnetic disk. The head is moved while floating from the surface of the magnetic disk.
If the surface of the magnetic disk is uneven, the head collides with the uneven surface when being moved, which damages the head and the magnetic disk. Further, in recent years, there has been a demand for greater storage capacities of hard disks by increasing the recording density. To meet this demand, the distance between a magnetic disk and the head must be minimized. Thus, glass substrates for data recording media used in magnetic disks are manufactured by subjecting the surfaces of glass substrates to a precision polishing. Accordingly, the smoothness of the glass substrate surfaces are improved to obtain even surfaces.
In the above polishing, a suspension, or slurry in which particles are dispersed in water, is used as a polishing agent. The main ingredients of the particles are cerium oxide and silicon dioxide. This is because the sizes of the cerium oxide and silicon dioxide are small and thus the cerium oxide and silicon dioxide have superior polishing efficiency to increase the smoothness of polished surfaces. Due to the recent widespread use of information technology devices such as computers, a significant number of magnetic disks are demanded. Accordingly, the amount of production per unit time needs to be increased. The amount of production can be increased simply by increasing the size of a polishing apparatus of glass substrates or by increasing the sizes of the particles. However, in these cases, the quality and the yield are lowered. It is therefore required to increase the amount of production while maintaining the quality.